Japanese Laid-Open Patent Publication No. 9-140453 describes an example of a toothbrush device that uses a potential gradient to improve a plaque removal effect. Such a toothbrush device includes a grip (main body) and an exchangeable brush member. A basal end of the brush member is connected to a distal end of the grip. A coupler shaft projects from the distal end of the grip. The brush member includes a receptacle formed in the basal end. The coupler shaft is inserted into the receptacle. Further, the coupler shaft has a basal end electrically connected to one of the electrodes of a battery, which is retained in the grip. When attaching the brush member to the grip, a distal end of the coupler shaft moves into the receptacle of the brush member to a position at which an electric terminal plate is located. An electric terminal accommodation chamber accommodates most of the electric terminal plate. However, the electric terminal plate has a contact that is exposed through an opening, which communicates the electric terminal accommodation chamber and the receptacle. Through this opening, the contact of the electric terminal plate resiliently contacts the distal end of the coupler shaft. The other electrode of the battery in the grip is electrically connected to an exterior electrode portion arranged on an outer surface of the grip. When a person brushes his or her teeth, the person's hand holding the grip touches the exterior electrode portion. This forms a closed circuit when the brush member comes into contact with the person's mouth. As a result, the battery sends a very weak current into the mouth via the coupler shaft and the electric terminal plate.